Where Do PM2.5 Particles Come From?​

Created By RISC | 7 months ago

Last modified date : 7 months ago

PM2.5 is a major issue in Bangkok every year. But do you know where the particles originate?

More than 57% of PM2.5 particles in Bangkok come from automobiles (46% diesel cars and 11% gasoline cars), with 22% from construction, industry, and agriculture. The remaining 21% are secondary particles formed by gases such as sulfur dioxide (SO₂) and nitrogen dioxide. When these gases are exposed to sunlight and heat, they undergo a reaction that produces more PM2.5. ​

The activities and environmental factors that cause PM2.5 occur primarily during the day. So why don’t PM2.5 levels drop at night? ​​
A study of PM2.5 during days with no air fluctuations found concentrations were highest at night from 7 pm to 6 am. The morning hours from 6 am to noon will be more intense from noon to 7 pm in Bangkok and in other provincial areas. ​

Meteorological conditions can be described using the ventilation flow rate (m²/s) based on wind speed (m/s) and atmospheric height (Planetary Boundary Layer (PBL) in meters. The PBL value represents the atmosphere near the earth's surface with turbulence due to the interaction of the ground and the lower atmosphere. Weather conditions with high PBL levels allow air to rise, lowering air pollution. If the weather has low PBL, the effect will be the opposite.​

High PM2.5 at night comes from daytime activities that couldn’t vent air because of the rapid decrease in ventilation rates. ​

PM2.5 density typically occurs from the night until the morning. During particle season, it is best to avoid exercising in the morning or late at night. Most importantly, before leaving the house each time, check the basic ventilation rate value from the Meteorological Department, which has a 7-day forecast, so you can deal with particles. ​

Check the ventilation rate value from http://ozone.tmd.go.th/Daily_VR.html​

Story by Napol Kieatkongmanee, Senior Sustainable Designer and TREES-A, Building Technology, Intelligent Systems, Innovative Solutions Specialist, RISC ​

References:​
Meteorological Department http://ozone.tmd.go.th/Daily_VR.html​
http://164.115.28.46/thaiexen/file_upload/submitter/file_doc/108864782a2b951d956f1a72ffcf0dfeb22b1.pdf​
Near-surface meteorological and air pollution measurement station Kasetsart University​